148 Transactions of the American Institute. 



and again another, and now we have an iron arch formed between the 

 poles, on which my assistant, as you see, can stand with perfect 

 security. He will now descend, and I will detach from the magnet 

 one of these wire ropes leading from the battery — the iron bridge 

 breaks and falls with a crash to the floor — an intensely brilliant flash 

 occurs at the point where I detached the battery-wire. And now 

 observe ; the iron cores are as powerless to hold this spike as they 

 were before the electric current enveloped them. 



As yet we have only experimented with fixed magnets. Let us 

 now see what will happen ro a magnet when I support it, so that it 

 can move freehy around its center of figure ; I have here two hard 

 steel plates ; one end of each is terminated in a spear, and in the 

 middle of its length is a little agate cup. I place on the horizontal 

 lens of the lattern this circular plate of glass, whose border, as you 

 observe on the screen, is divided into degrees. In the center of this 

 graduated circle I stand this little needle, and on it I rest one of these 

 steel plates. See, it turns freely round on its agate cup when I tap it 

 with my finger; and now I place its spear-end to any division of the 

 circle, and you see it remains there, and you observe that it has no 

 tendency, in itself, to point to one division in preference to any other. 

 I now replace it with this other similar plate or needle ; it behaves 

 precisely like the former one. I am now going to make these needles 

 magnets. What you see on the screen is the end of a steel magnet, 

 which is slowly stroking the supported needle from heel to spear-end, 

 and observe, I only pass the magnet over it in that direction. I now 

 have made several passes, and I lay aside the magnet and allow the 

 needle to take care of itself; see, how it is swinging forward and 

 backward, and, at last, its spear end has come to rest at thirty-five 

 degrees of the circle. I push it away from this position, but you 

 see it persists in returning to it. It now evidently has a preference 

 to remain in this diameter of the circle to any other, and we find on 

 examination that this diameter lies nearly in the north and south line 

 of the horizon. I now replace this by the other magnetized needle, 

 and you observe that it also remains pointing to any division to which 

 I direct it. I will also magnetize this needle by drawing over it in 

 the same direction, from heel to spool-point, the same end of the mag^ 

 net used in the previous experiment. I now remove my fingers from 

 the needle, and observe, it, also, is swinging to and fro, and gradually 

 it comes to rest, and now its spear-end is also pointing to thirty-five 

 degrees of the dial, and it returns to this division as often as I deflect 

 it from it. Thus, these experiments have clearly shown us that when 



